1. Field of the Invention
The present invention relates to a toner for use in a recording method employing an electrophotographic method, an electrostatic recording method, a toner jet system recording method, or the like, and more specifically, to a toner for use in a copying machine, a printer, or a facsimile, which forms a toner image on an electrostatic latent image bearing member in advance, transfers the toner image onto a transfer material to form a toner image, and fixes the transferred image under heat and pressure to provide a fixed image.
2. Description of the Related Art
In recent years, energy saving has been considered to be a big technical problem also in electrophotographic devices, and drastic reduction of calorie applied to fixing apparatuses has been mentioned as the energy saving in electrophotographic device. Accordingly, needs for so-called “low-temperature fixability” in a toner, in which fixing with lower energy is possible, have been increasing.
Conventionally, a technique involving increasing sharp melt property of a binder resin has been known as an effective method to enable the fixing at lower temperature. In this point, polyester resins have excellent characteristics.
In JP 2006-293273 A, there is proposed a capsule toner having a ratio of a storage elastic modulus of toner at 60° C. to a storage elastic modulus of toner at 80° C. (G′ (60)/G′ (80)) of 10 or more and 40 or less. However, when used in a high-speed device, the capsule toner shows low sharp melt property and insufficient low-temperature fixability in some cases.
On the other hand, as another viewpoint of high-quality image, reduction in the particle diameter and sharpening of the grain size distribution of toner have been proceeded for the purpose of attaining high resolution and high definition, and in addition, a spherical toner has started to be suitably used for the purpose of improving transfer efficiency and flowability. As a method of preparing efficiently spherical toner particles with small particle diameters, a wet method has started to be employed.
As a wet method capable of using a sharp-melting polyester resin, proposed is a “solution suspension” method of producing spherical toner particles, which includes dissolving a resin component in an organic solvent which is immiscible with water and dispersing the resultant solution into an aqueous phase to thereby form an oil droplet (JP 08-248680 A). According to the technique, a spherical toner with a small particle can be easily obtained, which uses polyester excellent in the low-temperature fixability as a binder resin.
Further, as the toner particle produced by the solution suspension method using the above-mentioned polyester as a binder resin, a capsule type toner particle is also proposed for the purpose of attaining additional low-temperature fixability.
JP 05-297622 A proposes the following method:
a polyester resin, a low-molecular weight compound having an isocyanate group, and another component are dissolved and dispersed into ethyl acetate to prepare an oil phase, and droplets are then prepared in water; then, the compound having an isocyanate group is subjected to an interfacial polymerization at a droplet interface, whereby a capsule toner particle having polyurethane or polyurea as an outermost shell are prepared.
In addition, JP 2004-226572 A and JP 2004-271919 A propose the following method: a toner base particle is prepared by a solution suspension method in the presence of resin fine particles formed of any one of a vinyl-based resin, a polyurethane resin, an epoxy resin, and a polyester resin, or those resins in combination, whereby toner particles having a toner base particle surface covered with the above-mentioned resin fine particles are prepared.
JP 3455523 B proposes toner particles obtained by a solution suspension method using a urethane-modified polyester resin fine particle as a dispersant.
WO 2005/073287 proposes a core-shell type toner particles formed of a shell layer (P) including one or more film-like layers each formed of a polyurethane resin (a), and a core layer (Q) including one layer formed of a resin (b).
The core-shell type toner particles having a constitution in which a core part has low viscosity and poor heat-resistant storage stability of the core part is compensated with heat-resistant storage stability of a shell part. In this case, a substance being relatively hard against heat is used as the shell part, and hence it is necessary to highly cross-link the substance and increase a molecular weight of the substance. As a result, there is a tendency to inhibit the low-temperature fixability.
On the other hand, monochrome printers have been apt to be reduced in size in view of personal uses and setting areas thereof in offices. Therefore, a one-component development system is preferably used owing to merit of reducing size of the device. The one-component development system includes: a magnetic one-component development system in which magnetic particles are incorporated in toner and a developer is carried and transferred by the magnetic action; and a nonmagnetic one-component development method in which a developer is carried on a developer carrying bearing member (developing sleeve) by a triboelectric charge action of the developer without using magnetic particles. The magnetic one-component development system does not use a colorant such as carbon black and can use the magnetic particle also as a colorant.
As the magnetic toner used in the magnetic one-component development system, various kinds of toners are proposed. For example, there are proposed a dry-type toner obtained by melting and kneading a magnetic powder in a binder resin and pulverizing the resultant, and, in JP 2003-043737 A, a toner obtained by a polymerization method involving dispersing a magnetic powder in a styrene-based resin as a result of a suspension polymerization is proposed. In addition, in JP 08-286423 A, a toner obtained by a solution suspension method using a polyester is proposed.
However, various problems are apt to occur in the magnetic toner using the solution suspension method. One of the reasons why the problems occur lies in that, when dispersion of the magnetic substance is insufficient, a large amount of the detached magnetic substance is apt to generate, resulting in deteriorating resistance of the toner. As a result, a toner charge quantity is reduced, and development defect, transfer defect, and the like are apt to be generated, and contamination of agents is easily caused. In addition, when an addition amount of a release agent is increased, the release agent is apt to appear on the toner particle surface, and an image quality is easily impaired due to flowability defect.
In addition, as means for improving an image quality in the electrophotographic processes such as developing and transfer, there are also studies on improving a developing performance and a transfer performance by controlling an adhesive force of toner.
However, most studies relate to an adhesive force between toner and a latent image-bearing member or members accompanied in a developing or transfer process. There are few studies discussing an adhesive force of the toner itself. For example, in JP 2006-195079 A and JP 2006-276062 A, an adhesive force between toner and carrier particles is proposed, but studies for improving the developing performance and the transfer performance due to the adhesive force of the toner in the case of using a magnetic toner have been insufficient.